A typical pumping cycle of a peristaltic pump operated at a constant speed throughout an entire cycle delivers fluid at different rates throughout the cycle. Particularly, linear peristaltic pumps act upon with a plurality of sequentially actuated pumping members to move a column of fluid through the tubing. The sequentially actuated pumping members progressively close the tubing from an inlet end toward a delivery end over a short length of the tubing. After one of the pumping members squeeze the fluid downstream toward the delivery end, the last pumping member in the sequence retracts from the tubing as the first upstream pumping element closes the tubing. The cycle is repeated with each sequential pumping element closing the tubing. The cycle is repeated toward the delivery end, thereby moving another column of fluid through the tubing for delivery. When the last pumping element in the sequence begins to lift off of the tubing at the delivery end, the tubing expands and the flow of fluid temporarily diminishes while the pumping column refills. This period of slowed or stopped delivery of fluid is sometimes referred to as a "dead band."
Also to a lesser degree, during other portions of the cycle, particularly immediately before and immediately after the dead band, the amount of fluid delivered is not precisely constant throughout the entire cycle. It is desirable to avoid the slow period of the dead band particularly when the volumetric flow is low.
Various control devices have been devised for controlling the drive motors at different speeds during the different portions of the cycle. Most such control devices require complex electronic controls or relatively expensive stepper motors with controls for varying the stepper speed.
In one such mechanism, a stepper motor having a first stepping speed outside of the dead band and having a second, faster stepping speed during the dead band, was provided by dividing one complete 360.degree. cyclic revolution of peristaltic pumping mechanism into the number of steps proportional to the angular duration of the dead band. For example, where the dead band exists during approximately 150.degree. of rotation and the stepper motor has approximately 200 motor steps for each full 360.degree. revolution of peristaltic drive shaft, the dead band corresponds to approximately 83 of the 200 steps of the stepper motor. A timing wheel is used comprising a transparent arc portion covering angular rotation of the wheel during which the stepper motor is to be operated at one speed and a second opaque arc portion corresponding to the angular rotation of the wheel during which the stepper motor is to be rotated at the second faster speed. Thus, a stepper motor is provided with two speeds of stepping. The transition from opaque to transparent is detected with a light sensor causing the stepping speed of the motor to transition from a first speed to a second speed. When the transition from the transparent arc to the opaque arc of the wheel is detected, the motor switched back to the first speed. This device also provided for the second sensor and a series of alternating opaque and transparent area throughout the slow pumping speed portion of the cycle for the purpose of checking for proper rotation direction. Such a device not only required a stepper motor having a variable stepping speed adjustable to correspond to the desired delivery rate and a maximum stepper speed that is activated each time the timing wheel indicates that the cycle of the pump is in the dead band. Moreover, this mechanism did not fully compensate for the variations of pumping rate during the period before and after the dead band. An attempt to compensate for these volumetric pumping rate variations was made by addressing a 150.degree. dead band with 138.degree. of the faster stepper speed, thus only approximating the actual variations of the rate of pumping.